چکیده انگلیسی

Thought blocks (TBs) are characterized by regular interruptions in the stream of thought. Outward signs are abrupt and repeated interruptions in the flow of conversation or actions while subjective experience is that of a total and uncontrollable emptying of the mind. In the very limited bibliography regarding TB, the phenomenon is thought to be conceptualized as a disturbance of consciousness that can be attributed to stoppages of continuous information processing due to an increase in the volume of information to be processed. In an attempt to investigate potential expression of the phenomenon on the functional properties of electroencephalographic (EEG) activity, an EEG study was contacted in schizophrenic patients with persisting auditory verbal hallucinations (AVHs) who additionally exhibited TBs. In this case, we hypothesized that the persistent and dense AVHs could serve the role of an increased information flow that the brain is unable to process, a condition that is perceived by the person as TB. Phase synchronization analyses performed on EEG segments during the experience of TBs showed that synchrony values exhibited a long-range common mode of coupling (grouped behavior) among the left temporal area and the remaining central and frontal brain areas. These common synchrony-fluctuation schemes were observed for 0.5 to 2 s and were detected in a 4-s window following the estimated initiation of the phenomenon. The observation was frequency specific and detected in the broad alpha band region (6–12 Hz). The introduction of synchrony entropy (SE) analysis applied on the cumulative synchrony distribution showed that TB states were characterized by an explicit preference of the system to be functioned at low values of synchrony, while the synchrony values are broadly distributed during the recovery state. Our results indicate that during TB states, the phase locking of several brain areas were converged uniformly in a narrow band of low synchrony values and in a distinct time window, impeding thus the ability of the system to recruit and to process information during this time window.

مقدمه انگلیسی

Thought blocking is a disorder of thought that is usually a sign of psychotic conditions and is characterized by regular interruptions in the stream of thought. Bleuler (1911) described how the phenomenon develops rapidly and occurs in transitory episodes of varying duration, with blocking not only of the stream of thought but of the entire psyche, involving the processes of attention, perception, memory, speech and motility. Outward signs are abrupt, repeated interruptions in the flow of conversation or actions. Subjective experience is that of a total, uncontrollable emptying of the mind. Blocking may give rise to the delusion that thoughts have been withdrawn from the head (thought withdrawal).
In psychiatric literature, TB phenomena are characterized as abnormalities of thought and, in the case of schizophrenia, are lumped together as formal thought disorder (a disorder in the form of thought, not the content) (McKenna, 1994). True thought blocking phenomena are rare (Andreasen, 1979) and must be distinguished from the occasional, benign loss of topic which occurs in normal individuals. Care must also be taken not to make the diagnosis of thought block when patients are simply distracted by their delusions or hallucinations.
A statistical perspective regarding the incidence of TBs among other thought disorder symptoms has been described in a study (Andreasen, 1979), where in 45 patients diagnosed with schizophrenia, thought blocking was found to be rare. Bleuler (1911) stated that the Kraepelinian concept of blocking was of fundamental significance in the symptomatology and diagnosis of schizophrenia. Since then, this view has been endorsed in some of the literature on schizophrenia, but the concept appears to have become limited to the sudden occurrence of stoppages in the flow of thinking. The phenomenon, so defined, has been likened to petit-mal epileptic seizures (Mayer-Gross et al., 1960). This peculiar phenomenon, in the case of schizophrenia, is bearing some resemblance to temporal lobe seizures. Both conditions appear to have a common denominator in terms of a paroxysmal impairment in consciousness. Consciousness has been said to depend largely upon the inter-relationship between the neural basis of the body schema and the perceptual organization of the environment, and also upon the capacity for memory storage of sensory data and the availability to recall stored information (Sherwood, 1957). In the same line of evidence, modern cognitive science posits that brain dynamics closely associated with cognitive processes involve synchronous neural oscillations occurring globally throughout the brain (Crick and Coch, 1998). Current views consider that EEG oscillations, with different spectral contents, recorded in various brain sites are assumed to play an important role in the information processes underlying cognition as well as the abnormal brain functioning observed in nosological entities that affect the neuronal connectivity such as schizophrenia and specific psychiatric symptoms such as hallucinations (Friston, 1998, Basar et al., 2000, Phillips and Silverstein, 2003, Uhlhaas et al., 2008, Angelopoulos et al., 2011 and Koutsoukos et al., 2013).
In bibliography, the absence of available data regarding the pathophysiology of the phenomenon may reflect the rarity of the symptom itself along with the methodological difficulties to study such a subjective experience. In the present study, we analyzed EEG oscillatory activity during the subjective experience of thought blocks in subjects suffering from persisting auditory verbal hallucinations. In these cases, TBs emerged automatically, in both under eyes open and eyes closed conditions, at distinct periods except for one case where TBs developed at the end of intense burst-like hallucinations. In the latter case, thought blocks marked the end of prolonged and intensive hallucinatory periods.